The Fischer esterification mechanism is examined in the following two questions in the assignment. Part 1 involves MeOH addition to form the key tetrahedral intermediate. Part 2 will involve loss of H2O to form the ester.

The mechanism is observed in the attached file.

Explanation:

It begins with the protonation of the carbonyl group of the carboxylic acid. Then, methanol attacks the protonated carbonyl group and forms a tetrahedral intermediate, which by a proton exchange process forms a tetrahedral intermediate that has water. The expulsion of water is produced by the regeneration of the carbonyl group, in addition to the formation of the protonated ester. Finally, the proton exchange with the water molecule regenerates the acid catalyst.

i think it's letter a.